When people view everyday scenes, their visual systems encounter far more information than can be fully processed. The brain uses attentional mechanisms to select important visual objects and filter out those that might be distracting. Mounting evidence suggests that the pulvinar nucleus of the thalamus plays a critical role in vision and attention, but its specific function is not understood. The pulvinar is interconnected with virtually the entire visual system, and is ideally situated to regulate visual cortical processing according to attentional demands. This proposal seeks to test the involvement of the pulvinar in regulating cortical processing during vision and attention. The first step toward this goal will be to characterize the interactions between neurons in the primate pulvinar and visual cortex using simultaneous, multi-site electrophysiological recording. By recording from dozens of sites within the pulvinar, visual cortical area V4, and inferior temporal cortex (IT), it will b possible to compare the timecourse of attentional modulation in each brain area, and measure functional interactions between neurons within and across areas. The timing of attentional effects, as well as the magnitude and directionality of neuronal interactions, will provide valuabl information about the function of the pulvinar and its connections with visual cortex. To test the causal role of the pulvinar in attentional control, novel optogenetics tools will then be used to transiently silence pulvinar neurons during visual attention. The nature of any deficits or differences in cortical activity during pulvinar silencing will highlight the contributions of the pulvinar to normal visual processes. The results of the proposed experiments will not only help the understanding of human attentional disorders, but also aid the development of advanced neural stimulation methods for use in visual prostheses for people with impaired vision. PUBLIC HEALTH RELEVANCE: Understanding the interactions between neurons during vision and attention will give important insight into the nature of attentional disorders and visual impairment. Furthermore, the development and use of new optogenetic tools for precisely manipulating neural activity will contribute to the design and creation of advanced visual prostheses.